A cryptic alien seaweed spreading in Mediterranean coastal lagoons.

Mediterranean coastal lagoons play a pivotal role in the environmental, social, and economic facets of the coastal areas.  In general, coastal lagoons serve as biodiversity hotspots, supporting diverse ecosystems, including wetlands, marshes, seagrass beds, and unique fauna. They function as carbon sinks, sequestering substantial amounts of atmospheric carbon dioxide. Coastal lagoons also act as hydrological regulators, serving as natural buffer zones during extreme weather events, regulating hydrological cycles, and minimizing the impacts of flooding.  Mediterranean coastal lagoons hold significant socio-economic value, providing essential fishing grounds and supporting local fishing communities, and as tourist. Finally, coastal lagoons have been integral to Mediterranean cultures for centuries, holding historical and cultural significance. Understanding the impacts of climate change on coastal lagoon is crucial for coastal planning and adaptation strategies. In this study artificial neural networks (ANNs)are applied to estimate the impacts of anthropogenic climate change on water masses characteristics of coastal lagoon. Specifically, ANNs are used to model the associations between climate variables and water mass properties (namely temperature and salinity), which can be used for future projections. The developed ANNs approach can be applied to generic coastal lagoons, if sufficient in situ data of temperature, salinity and sea level are available for developing the model. The driving meteorological variable can be extracted from meteorological reanalysis and model climate projections if their resolution is sufficient to describe the relevant mesoscale features. The method is applied to the Venice Lagoon, the largest Mediterranean lagoon. The Venice lagoon is an ecologically and socio-economically relevant environment with notable susceptibility and a comprehensive description of climate change impacts is essential for its conservation and sustainable management. An advantage of the Venice lagoon is the relative richness of in situ observations, because of extensive past field campaigns. Here we provide and estimate of the expected changes of its temperature and salinity that are produced by low and high climate change scenario, with corresponding uncertainties. The ANN was parameterized using a combination of field data of temperature, salinity, and sea level, along with reanalysis data for ground temperature, wind speed (v and u components), temperature at 2 m, precipitation, evaporation, and humidity. Field data were obtained from a 10-year monitoring campaign, during which 30 stations within the lagoon were sampled. Reanalysis data were downloaded from the Copernicus ERA5 database. The climate scenarios used for projections were obtained from the Med-CORDEX network.

Jellyfish degradation in a shallow coastal Mediterranean lagoon

Seagrass meadow degradation and loss is one of the major threats to fish biodiversity in coastal marine and lagoon ecosystems in the Mediterranean. Pipefishes and seahorses (family Syngnathidae) are particularly affected by loss of seagrass meadows and other structured habitats, on which they rely for survival and reproduction. Despite their charismatic appearance and peculiar behaviour, their habitat ecology is still poorly understood in Mediterranean coastal waters. This study focuses on syngnathid assemblage composition and diversity in the shallow waters of the Venice lagoon (Italy), aiming at highlighting habitat preferences and providing insights into the conservation of biodiversity in these ecosystems. Generalized Additive Models were used in order to disentangle the potential effect of habitat typologies and different architectures of seagrass meadows from that of other environmental parameters. Most abundant taxa and whole syngnathid assemblage indicators were positively associated with seagrass meadows. Only few species, however, were seagrass specialists in shallow waters, and preferred meadows with taller canopies. Despite that, other structured habitats including short‐leaved seagrass meadows and macroalgal beds were important for some species and overall assemblage diversity. Managers in Mediterranean coastal lagoons should thus limit human pressures that lead to the depletion of seagrass meadows, with particular attention to long‐ and broad‐leaved species in less confined areas. Nevertheless, syngnathid assemblages would benefit from the preservation and restoration of the overall habitat diversity characterizing shallow waters in coastal lagoon. Future studies should aim at investigating the potential role of habitats at greater depths in supporting syngnathids.

1 - Phytoplankton observations are commonly used to contribute to the assessment of aquatic ecosystem health and their trophic status. Compared to other methods, chemotaxonomic analysis based on High Pressure Liquid Chromatography (HPLC) presents many advantages (e.g., rapidity, reproducibility, and capacity to include pigments from all cell sizes), but its use in coastal lagoons studies is still not very common. The method of Wright et al., (1991) recommended by the UNESCO (Jeffrey et al., 1997) and most frequently used for phytoplankton analysis in coastal lagoons, so far, was selected and compared to the more novel method of Hagerthey et al. (2006). 2 - The two methods that differed slightly with respect to their solvent gradients during chromatography (mobile phase) and column (stationary phase), were tested using a pigment mix from DHI Water and Environment comprising 30 different pigments. Extraction methods were tested using replicates of 1l of sub-surface water from the Thau lagoon (South of France), sampled in June 2013. Optimization of the extraction was performed by testing different volumes of solvent (2 to 5 ml), different solvents based on a mix of methanol, acetone, dimethylformamide, water, compared to acetone 90% and pure methanol, as well as different extraction times (10 min to 2 h), and the addition of the ion-pairing agent tetrabutyl ammonium acetate hydroxide (TBAA). 3 - The second method of analysis allowed better separation and resolution of most of the pigments, especially of lutein and zeaxanthin. The early-eluting most polar pigments and the more hydrophobic pigments eluting in the end of the chromatogram (chlorophylls and carotenoids) showed also better separation and peak shapes. 5 mL of the mix of acetone/ methanol/ water (45:45:10) allowed the best extraction of the pigments. The use of TBAA showed negative effects. 4 - For pigment analysis in coastal lagoon, our final protocol used 1 h extraction with 5 mL of acetone/ methanol/ water, and analysis with the gradient from Hagerthey et al. (2006). On our analytical equipment it needed some adjustments. It uses a longer chromatography run and quantified the phytoplankton pigment markers better than the method of Wright et al. (1991).

Fifty years of ecological changes: Regime shifts and drivers in a coastal Mediterranean lagoon during oligotrophication

Influence of nitrogen enrichment on size-fractionated in vitro carboxylase activities of phytoplankton from Thau Lagoon (Coastal Mediterranean Lagoon, France)

Biogeochemical and contaminant cycling in sediments from a human-impacted coastal lagoon – Introduction and summary

Optical characterization of coastal lagoons in Tunisia: Ecological assessment to underpin conservation

To investigate the responses of a natural microbial plankton community of coastal Mediterranean waters to warming, which are still poorly known, an in situ mesocosm experiment was carried out in Thau Lagoon during autumn 2018. Several microorganisms, including virio-, bacterio-, and phytoplankton < 10 µm in size, were monitored daily and analysed using flow cytometry for 19 consecutive days in six mesocosms. Three mesocosms (control) had the same natural water temperature as the lagoon, and the other three were warmed by + 3 °C in relation to the control temperature. The cytometric analyses revealed an unexpected community dominated by picophytoplanktonic cells, including Prochlorococcus-like and Picochlorum-like cells, which had not previously been found in Thau Lagoon. The experimental warming treatment increased the abundances of nanophytoplankton, cyanobacteria, bacteria and viruses during the experiment and triggered earlier blooms of cyanobacteria and picoeukaryotes. Only the abundance of Picochlorum-like cells was significantly reduced under warmer conditions. The growth and grazing rates of phytoplankton and bacterioplankton estimated on days 2 and 8 showed that warming enhanced the growth rates of most phytoplankton groups, while it reduced those of bacteria. Surprisingly, warming decreased grazing on phytoplankton and bacteria at the beginning of the experiment, while during the middle of the experiment it decreased the grazing on prokaryote only but increased it for eukaryotes. These results reveal that warming affected the Thau Lagoon plankton community from viruses to nanophytoplankton in fall, inducing changes in both dynamics and metabolic rates.

Diversity of property regimes of Mediterranean coastal lagoons in S. France; implications for coastal zone management

AimUnderstanding and quantifying the seasonal patterns in biodiversity of phytobenthos, macro‐zoobenthos and fishes in Mediterranean coastal lagoons, and the species dependence upon environmental factors.LocationThe study was carried out in the “Stagnone di Marsala e Saline di Trapani e Paceco,” the largest coastal lagoon system in the central Mediterranean Sea (Sicily, Italy), a Special Protection Area located along one of the central ecological corridors joining Africa and Europe.MethodsThe coastal lagoon system was selected as a model ecosystem to investigate the seasonal variations in biodiversity indices and dominance–diversity relationships in phytobenthos, macro‐zoobenthos and fishes, and how seasonal variations in temperature, salinity, depth, inorganic and organic suspended matter affect the abundance of the species constituting these communities. Models of ecosystem structure, describing the interactions among functional groups and environmental variables, were also developed using confirmatory path analysis and artificial neural networks to exemplify their application in predicting temperature‐driven alterations.ResultsWide seasonal variations in biodiversity indices and dominance–diversity relationships across the communities of the coastal lagoon system were observed, driven by the dynamics in climate and resource availability. The effects of the environmental variables on taxon abundances varied in relation to the community, with the widest responses elicited in phytobenthos and fishes. Temperature was the main variable affecting taxon abundances in macro‐zoobenthos and was also the major driver of shallow water ecosystem structure.Main conclusionsThis research shed light on the seasonal variations in biodiversity of Mediterranean coastal lagoons, elucidating also the tight dependence of phytobenthos, macro‐zoobenthos and fish diversity upon environmental factors. The findings and the methodological approach proposed may be crucial in developing models able to predict future climate‐driven alterations in communities inhabiting these important and threatened ecosystems.

Nutrient overload promotes the transition from top-down to bottom-up control and triggers dystrophic crises in a Mediterranean coastal lagoon

To better identify the responses of phytoplankton blooms to warming conditions as expected in a climate change context, an in situ mesocosm experiment was carried out in a coastal Mediterranean lagoon (Thau Lagoon, South of France) in April 2018. Our objective was to assess both the direct and indirect effects of warming on phytoplankton, particularly those mediated by top-down control. Four treatments were applied: 1) natural planktonic community with ambient water temperature (C); 2) natural planktonic community at +3°C elevated temperature (T); 3) exclusion of larger zooplankton (> 200 μm; mesozooplankton) leaving microzooplankton predominant with ambient water temperature (MicroZ); and 4) exclusion of larger zooplankton (> 200 μm; mesozooplankton) at +3°C elevated temperature (TMicroZ). Warming strongly depressed the amplitude of the phytoplankton bloom as the chlorophyll a concentration was twice lower in the T treatment. This decline under warmer conditions was most likely imputed to increase top-down control by zooplankton. However, removal of mesozooplankton resulted in an opposite trend, with a higher bloom amplitude observed under warmer conditions (MicroZ vs. TMicroZ) pointing at a strong interplay between micro- and mesozooplankton and the effect of warming for the spring phytoplankton blooms. Furthermore, both warming and mesozooplankton exclusion induced shifts in phytoplankton community composition during bloom and post-bloom periods, favoring dinoflagellates and small green algae at the expense of diatoms and prymnesiophytes. Moreover, warming altered phytoplankton succession by promoting an early bloom of small green flagellates, and a late bloom of diatoms. Our findings clearly highlighted the sensitivity of phytoplankton blooms amplitudes, community composition and succession patterns to temperature increases, as well as the key role of initial zooplankton community composition to elicit opposite response in bloom dynamics. It also points out that warmer conditions might favor dinoflagellates and small green algae, irrespective of zooplankton community composition, with potential implications for food web dynamics and energy transfer efficiency under future ocean condition.

Molecular approach indicates consumption of jellyfish by commercially important fish species in a coastal Mediterranean lagoon

Aerobic anoxygenic phototrophic (AAnP) bacteria are bacteriochlorophyll a (BChl a)- containing prokaryotes that can use both dissolved organic matter and light as energy sources. AAnP bacteria are widely distributed in aquatic environments where they are expected to play an important role in carbon cycling. However, little is known about their spatio-temporal distribution in marine ecosystems. In this study we examined the dynamics of AAnP bacteria in a coastal saline lagoon from November 2007 to September 2008. AAnP cells were enumerated by infrared (IR) microscopy, and BChl a concentrations were measured by both IR kinetic fluorometry and high-performance liquid chromatography (HPLC). The distribution of AAnP bacteria varied seasonally, but no clear spatial pat- tern emerged. The abundance of these bacteria ranged from 1.0 to 13.5 × 10 4 cells ml -1 from winter to summer, comprising 0.1 to 3% of total bacterial abundance. Size fractionation of the BChl a fluores- cence signal showed that AAnP bacteria were mainly particle-attached in winter and free-living in spring and summer. BChl a concentrations (up to 108.7 ng l -1 ), BChl a content per cell (up to 1.7 fg cell -1 ) and the ratios of BChl a to chlorophyll a (chl a) (up to 15%) were high in spring and summer, suggesting that AAnP bacteria contributed significantly at this time to photosynthetically driven en- ergy production in the lagoon. Temperature and light were the main factors driving seasonal varia- tions in the abundance of AAnP bacteria, while total bacterial abundance was closely related to varia- tions in the concentration of dissolved organic carbon. These results highlight for the first time the numerical importance and the dynamics of AAnP bacteria in a coastal lagoon.